The invention relates to a method of treating aqueous materials. It is particularly applicable to clarified sludge such as that which is obtained in large amounts in the operation of clarifying plants for treating municipal and industrial effluent, but can also be applied to similar aqueous materials, for example, those having a relatively high ash content, such as organic waste in aqueous suspensions, wet peat, or wet wood shavings or chips.
Sometimes it is possible to apply a clarified sludge directly to agricultural land, as a decomposed thin slurry. However, a number of problems and costs are involved, with regards to the rotting required, the sterilization, packaging and transport. Many clarified sludges are also contaminated with heavy metals, poisons and environmentally unacceptable substances, which means that they cannot be used in this way.
The above use is also impossible in heavily populated areas with large sludge output, since too much demand is made of the transport or of the available agricultural land which is economically accessible. Thus, it has been proposed to thicken or even dry the clarified sludges or other similar materials obtained and to apply them to agricultural land in this form. Also, particularly where such application is not possible owing to the presence of pollutants or for other reasons, it has been proposed to burn the sludges, optionally mixed with a fossil fuel.
These processes have a variety of disadvantages with regard to pollution from the product itself or from the operation of the treatment plant, mostly as a result of pungent-smelling exhaust gases or even exhaust gases which are harmful to health. Their economic viability must also be taken seriously into consideration.